ECE 3042
Spring 2013 Homework No. 1 for Exp. No. 1
Due Week of January 21
1. Shown below is a single stage common emitter amplifier using an 2N3904 NPN BJT as the active device.
Design the circuit so that it clips symmetrically, viz. pick RB1 and RB2 so that the collector current is that which
yields symmetric clipping. The design specification for the magnitude of the small signal midband voltage gain is 33.
For the design calculations assume the the base-to-emitter dc voltage drop is 0.65 V, that the current in RB1 is 10IB ,
β = 200, the base spreading resistance is 10 Ω, and the Early voltage is infinity.
2. For the circuit parameters indicated in the diagram, use National Instruments SPICE to
determine:
• the dc operating point of the circuit, viz. the dc voltage at each terminal of the transistor and the current owing
into the collector and base leads and out of the emitter.
• the small signal ac voltage gain, viz. a plot of the gain, Av versus frequency where the frequency range is from
10 Hz to 100 MHz.
• the positive and negative clipping levels, viz. the maximum and minimum possible values of the output voltage,
vo .
• plot of the output voltage versus time for 2 cycles of the input for an input signal with a frequency of 1 kHz and a
peak value 0.1, 0.3, and 1 V.
• plot of the output voltage versus frequency for a frequency span from dc to 10 kHz, viz. a spectral analysis. Plot
the output voltage on a log scale for each of the three input levels used in the previous step. Compute the THD
for each.
Assume that the SPICE parameters for the 2N3904 NPN BJT are: saturation current, 10 f A; forward
beta, 200; Early voltage, 170 V, zero-bias base collector capacitance, 3.6 pF; forward transit time, 0.3 ns, and base
spreading resistance, 10 Ω. (These are the values given in the model statement on page 7 of Experiment 1.)
3. Verify the SPICE solution for the above with a hand calculation using the parameters given for the SPICE
simulation. Calculate the dc operating point, mid-band small signal voltage gain, and positive and negative clipping
levels.
V + = 30 V
V+
6.8k Ω
R
R
vi
v
G
B2
C1
C
C2
10 μ F
RL
0.22 μ F
RB1
vo
22k Ω
R
E1
220 Ω
R E2
C
E
100 μ F